Bi-directional communication devices, such as cable modems, have been designed to specifically operate under a single standard, such as the North American Data Over Cable Service Interface Specifications (DOCSIS®) or the European DOCSIS® standards. The European version of the North American DOCSIS® standard was not available when DOCSIS® was first proposed to European customers. Many European cable operators started deploying the North American DOCSIS® standard. They now express the need to change to a European DOCSIS®-compliant system.
There are three main differences between a European DOCSIS® cable modem and a North American DOCSIS® cable modem. First, a diplexer within the cable modem has a different cross over point in the European and North American systems, since the forward (downstream) and the return (upstream) data channel bandwidths on the coax cable are slightly different. This difference in diplexer crossover point is realized by different high pass filter and low pass filter cutoff frequencies between the European and North American systems. Second, the forward data channel is 8 MHz wide for European DOCSIS®, while in the North American DOCSIS® the forward data channel is 6 MHz wide. This requires a different surface acoustic wave (SAW) filter to maximize performance when additional channels are located next to the desired channel without any guard band. Third, the forward data channel for the European DOCSIS® uses a different forward error correction (FEC) scheme than is used in the North American DOCSIS®. Providing a single cable modem that could operate under both the North American and European standard systems would reduce the costs for the manufacturers, re-sellers, and renters by economy of scale.